Stereo sound recording on super-8 motion picture film



June 24, 1969 D. HAFLER STEREO SOUND RECORDING ON SUPER8 MOTION PICTURE FILM Sheet LHZ MAG SOUND HEAD Filed Oct. 4, 1965 I f?6 AMP -0I 2 27 2 AMP MATRM LHZ AMP L- 2 MAG .souuo HEAD INVENTOR ST AG'GEQD Mamas ATTORNEYS June 24, 1969 Filed Oqt. 4, 1965 HAFLER Sheet 3 AMP OUTPUT TRANSFORMERS g (IT-28%| 64 I2 AMPL W2 $16.5 @123?) Ahpu(L L?3 ABC Mmmx L26 AMP L 31.5.7 Q 9 52% H 92 L94 6 MATRM 8 100 R L R BYAS H2 AMP A Mp 05c *Q INVENTOR DAV") HAFLER BY x 60L,

' ATTORNEYS United States Patent 3,452,161 STEREO SOUND RECORDING ON SUPER-8 MOTION PICTURE FILM David Hafler, 11 Merion Road, Merion Station, Pa. 19066 Filed Oct. 4, 1965, Ser. No. 492,630 Int. Cl. G03b 31/02 US. Cl. 179-100.2 6 Claims ABSTRACT OF THE DISCLOSURE The present invention relates generally to sound recording, and more particularly, to stereophonic sound systems for use with motion picture equipment.

Motion picture equipment, i.e., cameras and projectors, designed for the amateur, normally utilize a relatively small width film strip of either 8 mm. or 16 mm. size; the 8 mm. width being, by far, the most popular and most widely used for home movies. Because of the relatively small size of such film, the introduction of a sound recording medium thereon has generally presented certain design problems in providing the necessary sound track width in the limited space available.

Motion picture film of 8 mm. width, having a single magnetic sound track, is presently commercially available, and such film has a single track of magnetic material, generally composed of a magnetizable oxide, disposed between one edge of the film and the sprocket holes located therein. Such film has only sufficient space for said one sound track and the modification of such film to provide a second track for stereophonic sound reproduction would ordinarily pose extremely severe design problems.

Recently, a somewhat different format has become commercially available in 8 mm. motion picture film. Such film, and associated equipment for use therewith, has been sponsored by the Eastman Kodak Company and is termed Super-8. This motion picture film is characterized, inter alia, in that the area of each frame, for visual presentation, is greater than that of the conventional 8 mm. film. Also, the orientation and size of the sprocket holes has been changed to provide a greater amount of usable width. Further, and most significant for the purposes of the present invention, a sound reproduction medium comprising a magnetic stripe is provided along one edge of the film; however, in this case, the magnetic stripe is disposed between the film edge and the visual frame, instead of between the opposite film edge and the sprocket holes. By so locating the sound track adjacent the edge of the film opposite the sprocket holes, it is then required to provide the film with mechanical balance for winding purposes. This is conveniently accomplished by coating a second stripe of material, similar to that used for the sound track, along the edge of the film adjacent the sprocket holes in the very narrow space there provided. The balance stripe width may be anywhere from approximately 20 to 65 percent of the Width of the sound track and is coated generally in an inferior manner with respect thereto, so as not to be generally considered usable for satisfactory sound reproduction; the sole purpose of such stripe being for winding balance.

In accordance with the present invention, it has been discovered that both the normal sound track and the balance stripe found in the Super-8 format are capable of being used to achieve high fidelity stereophonic sound reproduction, heretofore not considered feasible, since even the Super-8 format has insufficient space to accommodate the two regular width sound tracks normally expected to be necessary.

The present invention provides a sound recording and reproduction system whereby the two signal channels required for stereophonicsound recording, i.e. the left and right channels, are so combined such that a first signal, representing the sum of the left and right channel signals, is recorded on the sound stripe of normal width and a second signal, representing the difference between the left and right channel signals, is recorded on the narrow stripe. Magnetic pickups are provided for each respective stripe whereby the separate sum and difference signals are amplified. After being amplified, each of the sum and difference signals are fed'to a matrix arrangement which decomposes the sum and difference signals into the left and right channel components. Of course, the left and right channel components might, alternatively, be separated by a simplexing technique or any other technique known to the art. The left and right channels, after being optionally amplified, feed electroacoustic translating means, such as loudspeakers, spaced so as to provide the desired stereophonic effect.

The system of the present invention produces sound reproduction of high-fidelity quality, while achieving a stereophonic effect with a recording medium generally considered insufficient for this purpose.

In addition, the system, in accordance with the present invention, retains compatibility with monaural systems of the conventional type.

The recorded sum signal provides the signal components necessary for high fidelity reproduction, while the difference signal, even though recorded on an extremely poor reproduction medium, supplies the components essential for good stereophonic effect. The narrow balance stripe, when used for magnetic recording, is generally characterized by a limited and narrow range of frequency response and a low signal to noise ratio which renders a rather degraded quality of sound reproduction.

However, it is generally found that the low frequency acoustic wave components are relatively nondirectional. Further, these components of the left and right channel signals normally have amplitudes which are approximately equal. Thus, typically the difference signal of (LR), at low frequencies, will have relatively small amplitudes as compared wit-h the sum signal of (L+R), and some loss thereof in reproduction will not materially affect the fidelity, which will then depend almost entirely on the quality of the sum channel signal.

At the other end of the acoustical frequency spectrum, it is generally found that at frequencies above about 10,000 cycles, the wavelength of the sound is about equal to or less than the inter-ear spacing of the average listener and thus, at these frequencies, the location of the source becomes not readily asc'ertainable. Therefore, the loss of these high frequency components can also be tolerated, if this loss occurs only in the difference channels. Thus, the low and the high frequency components are not materially significant with respect to the subjective stereophonic effect on the listener.

The fidelity of the recording and reproduction is retained by the sum channel signal which is recorded on the normal sound track of the film and which supplies a left and right channel signal of good quality, including those frequency components which might be lost in the difference channel.

Because of the above-stated limitations of the difference channel, electrical components which have resnicted"bandwidths'andlovverpower'ratings; as compared "or stereophonicmotionpicture equipment designed'for'the Super-8 format. In addition, the stereophonic" sound-"systern, in-accordance" with the present invention, iscapabl'e of use with dualmotion picture equipment designed to be iise'd'wi th either the'conventional 8 .willfihereafter bedisc'us'sed:- I

AL further feature, in'aCcorda'n'ce with the present inve'ntion; is the "provision for dynamic expansion or contraction of -the"L'R chan'nel'.This feature provides mm; or Super-8 film, as I greater enhancement of the fidelity of reproduction and 1 "comprises means fore diminishing, or eliminating completely, the L-R'si'gnal whenever the L+R signal is at a relatively low amplitude level. When the L+R signal is eta-relatively high, -or normal level, the LR signal is maintained at itsnormal level. Inthis manner, the effects fof"thexinferior signal-to-noise ratio of the LR channel can be diminished. Thus, for, low level signals,'the (L R') signalwould disappear, producing no stereo effect, but providing'the system with an improved signalto-no'ise ratio. The lack of stereophonic separation does not represent a serious disadvantage in this instance because it does not appear to be important at low signal levels. Still another feature, in accordance with the present invention, is the provision of a matrix system for decomposing, or separating the sum and difference signals into the left and right channels, wherein the loudspeakers are brought into,and made directly a part of the system resulting in the elimi.1ation of the additional transformers normally employed in conventional matrix arrangements and thus, producing even greater economies in the system. Accordingly, it is 'an object of the present invention to achieve stereophonic sound reproduction utilizing the limitedrecording medium characteristic of amateur motion picture film.

It is another object of the present invention to utilize a motion picture film having magnetic stripes of unequal width for compatible stereophonic sound reproduction.

It is a further object of the present invention to provide a system whereby the sum and difference of two stereo- .phonic sound signals are recorded and reproduced on separate-sound tracks of different widths.

It is still another object of the present invention to utilize the magnetic balance stripe on motion picture film for .sound reproduction in a high fidelity stereophonic sound system, not heretofore achieved.

"Still. another object of the present invention is to provide a sound motion picture system which is compatible for monaural and stereophonic sound reproduction in addition to being capable of use with motion picture equiptment designed for use with 8 mm. motion picture" film 5 having either the conventional or Super-8 format. --Still a further'object of the present invention is to provide a reliable, compatible stereophonic sound record.- ing system capable of high fidelity rep'r oduction'aricl being economical to manufacture. Y

The above and still further objects, features and advantages: of thepresent invention will become apparent upon consideration of the following detailed description of several specific embodiments thereof, especially when taken in' conjunctionwith the accompanying drawings,

wherein: a

FIGURE 1 shows the various motion picture fil m formats and pickup head loca't'ons in accordance with the .present invention; A

FIGURE 2 illustrates, in block diagram farm, a So nd system in'accordance' with oneembodiment of the present invention; 1

FIGURES'illustrate's'the general environment ofthe present invention;

FIGURE 4 illustrates one example of a matrix arrangement usable in the present invention;

FIGURE 5 illustrates,'in-block diagram form, a sound system in'ab'co'rdance'lwith asec ond embodiment of the present inventioh; p "I FIGURE 6"illu strates,a second matrix arrangement in accordance,withjanqther. embodiment ofthe inventionpand FIGURE '7 illustrates .theblock diagram of a general recording system. in accordance with the present invention.

Referring now to FIGURE 1, there is shown a comparison of' they conventional 8 .film format with that of ,theSuper 8 and the, arrangement of sound pickup heads, in relation thereto, The conventional .8 mm. film is shownflin, FIGURE ,1.(a) having a .total width of nominally 0.315 inch. A magnetic stripe z of about 0.03 inch is coated on thefilm base 1 between edge 16' and sprocketholes 3. The conventional motion picture sound system provides a certain lagv between the visual information of a particular frame and the corresponding sound portion on the magnetic stripe. The magnetic sound head 10, which maybe of any conventional type, is thus located at a certain predetermined distance along the transport path fromfthe projector (or camera) aperture.

FIGURES 1(b) and 1(c). show the format of the Super-8 'film which has the same nominal width as the conventional type. Each frame 7, for presenting the visual information, has a larger area than the frame 4 of the conventional film, the sprocket holes .being reoriented in order to provide more usable width. The sound track 8, corresponding to sound track 2 of FIGURE 1(a), is shown relocated on the opposite side of the film between filr'rl edge 17 and the frame 7, Where edge 18 of the Super 8 format corresponds to edge 16 of the conventional forlnat. Ajspaceof. about 0.020 inch remains between the sprocket holes 6 and the edge 18..Because the magnetic sound stripe 8 is located at a relatively large distance from the sprocketholes rather than, as heretofore, being adjacent thereto, an additional stripe may be applied in the aforementioned space between the holes 6 and the edge 18 to mechanically balance thefilm and to provide uniform winding.,-'1"he balance stripe 9 is deposited for thisreason, and primarily for manufacturing convenience consists essentially of, the magnetic oxide material of which the sound track 8.is composed. However, the width of .the stripe 9fmay range from only 0.006 to 0.018 inch and the care with which application is made is generally less than that for the normal soundtrack 8. Consequently, if the balance stripe 9 is used as a recording medium, the sound reproduction will be of a degraded'nature having a relatively low signal-to-noise ratio. However, by using the balance'stripe 9 in conjunction with the sound track 8 inthejsystem of the present invention, high fidelity sound reproduction may be achieved in addition to providing a stereophonic effect for the reasons previously stated.

Referring toFIGURE 1(c), a signal which contains the sum of the Left-and Right channel signals is recorded on the, regular magnetic sound track 8, while another signal which contains the difference between the Left and Right channel signals is recorded on the narrow balance stripe 9. .Magnetic pickup'heads 13 and 14 are located adjacent each respective stripe and at a given predetermined dis- .tance'along the transport path from the aperture, correponding;to the amountof lag required. The motion picture equipment designed toutilize the Super 8 format requires a, shorter. lag than the equipment designed for use with the conventional soundfilm of FIGURE 1(a), .andthus the heads.13 and 14 are illustrated as being in a relatively higher position, assuming the film is to move toward the bottom of the figure.

' Alternatively, instead of two separate pickup heads, a single head 15 with two in-line magnetic gaps might be used. This, of course, simplifies the construction of the unit and also the adjustment of the required lag for each stripe.

FIGURE l( b) shows a modification of the arrangement of FIGURE 1(c) which adapts the system of the invention to a dual projector capable of handling either of the two aforementioned film formats. A first magnetic pickup 11 is provided and arranged so as to respond to the sound track of the conventional 8 mm. film of FIGURE 1(a) with the proper lag bet-ween the visual and audio information therefor. A second magnetic pickup 12 is provided opposite the first head and in staggered relation thereto in order to respond to the sound track of the Super 8 film which has a shorter lag and is disposed on the opposite edge of the film. Now, by utilizing the head 12, normally associated with the Super 8 format, for the sum Signal and the head 11, normally associated with the conventional format, for the difference signal recorded on the narrow or balance stripe of the Super-8 format, a dual projector of the type described may be incorporated into the system of the invention. Of course, it is required that a suitable lag and stagger be used in the recording arrangement for each stripe. Generally, an adjustment of the heads would be necessary in order to bring about the proper relative stagger.

A. sound system, in accordance with the present invention, is shown in FIGURE 2 comprising magnetic pickup heads 21 and 22, each responsive to the (L+R) and (LR) stripes, respectively. Each head is electrically connected to an audio amplifier, the outputs of which are fed to a matrix 25. The function of the matrix is to separate the sum and difference input signals and provide Left and Right channel outputs which are amplified by amplifiers 26 and 27. Various simplexing circuits might also be used to perform the same function and the particular circuits disclosed are not to be considered in a limiting sense.

The output signals from the Left channel and Right channel amplifiers are each fed to the loudspeakers 28 and 29 which are arranged to provide a stereophonic separation.

The amplifiers 23, 24, 26 and 27 may be of any conventional type, however, since the (LR) signal has a narrower bandwidth requirement, amplifier 24 may have a correspondingly narrower bandwidth and a lower power rating.

The matrix may comprise any of the arrangements known in the art, an example being that shown in FIG- URE 4. The particular prior art circuit of FIGURE 4 is merely included as exemplary in the description of the system of the present invention and is shown to comprise two transformers 41 and 42, each having double primary windings 43, 44, 46 and 47 and single secondary windings 45 and 48. The primary windings 43 and 44 of transformer 41 are both wound with the same sense, while the primary windings of transformer 42 are wound with opposite senses. The secondary windings-45 and 48 are connected in series and a ground connection is provided therebetween. Then, if the (L+R) signal is applied to winding 43 and the (LR) signal is applied to winding 44, the output of the transformers will provide separate signals proportional to the Left and Right components of the sum and difference inputs.

FIGURE 7 shows a simple exemplary system for recording the appropriate signals -on the motion picture film. Left and Right stereophonic channel microphones 92 and 93, respectively, receive the program material to be recorded, which is amplified by amplifiers 94 and 95. The outputs of these amplifiers are fed to a matrix 96, which may be similar to that used in the system of FIGURE 2, and which, in turn, feeds the separate sum and dilference amplifiers 97 and 98. Recording bias is provided by the bias oscillators 99 and 100 which is applied to the amplifier outputs. Each signal is then fed to the magnetic recording heads 101 and 102, which, of course, may be two in-line gaps of a single head, if desired.

The recording system may be located at the camera site and/or at the site of projection for program recording, correction and narration. In this respect, means for magnetic erasure may additionally be provided as is well known in the art.

FIGURE 3 shows a motion picture projector incorporating the features of the present invention and is merely intended to illustrate one example thereof. Film 91, which is wound on reel 31 is threaded over guide rollers 33 and 34, and over sprocket wheel 35, through loop formers 81 and 82, and over sprocket wheel 37. The film then runs on guide rollers 36 and72 over the magnetic pickup heads 21 and 22, on roller 71 and over sprocket wheel 38. The film is then taken up on reel 32. The rollers 71 and 72, together with the guidepost 73 retain the magnetic stripes against the heads with the proper pressure by means well known inthe magnetic recording art.

The heads 21 and 22 are illustrated in the aforementioned staggered arrangement shown in FIGURE 1(b). Head 22 is positioned to respond to the (L+R) signal recorded on the wide .magnetic stripe and head 21 is positioned to respond to the (LR) signal recorded on the narrow magnetic stripe. The relative distances of each head from the projection aperture must correspond to the relative distances of the respective magnetic heads of the recording device so that the same head displacement exists for recording and playback.

FIGURE 5 showns another embodiment in accordance with the present invention. The system shown in FIGURE 5 is similar to that shown in FIGURE 2, like elements being identified by the same numerals, however, the system of FIGURE 5 includes the further feature of dynamic expansion and contrac ion of the (LR) signal for the reasons aforesaid. This is accomplished, for example, by utilizing an automatic gain control circuit (AGC) 30, of any well known construction which, in response to a decrease in the amplitude of the (L+R) amplifier 23 output, produces a signal which reduces the gain of the (LR) amplifier 24. Further, the amplifier .24 may be biased such that it is completely cutoff when the output of amplifier 23 is below a predetermined level. In this manner, the eifect of the low signal-to-noise ratio of the (LR) signal is substantially reduced, resulting in an improvement in the signal-to-noise ratio for the .overall system.

turn, is connected in series with loudspeaker 66 and ;the secondary 63 through leads 60 and 69. The secondary 64 of transformer 62 has one end connected to ground and the other end connected to lead 60 interposed between the two speakers 65 and 66. In this manner, lead 67 carries a signal of +(L-j-R); lead 69 carries a signal of -(L-|-R); and winding 64 carries a signal of (LR). Thus, by algebraically combining the signals, it is easily seen that speaker 65 receives only the Right channel signal and speaker 66 receives only the Left channel signal.

The need for the additional matrix transformers 41 and 42, as shown in the circuit of FIGURE 4, is thus eliminated and the matrix is achieved by merely incorporating the two speakers into proper circuit arrangement with a centertapped output transformer of the sum channel amplifier. This results in a final unit construction which has the advantages of being extremely compact, relatively easy to assemble, and relatively economical to manufatcure, while still maintaining compatible stereophonic high fidelity reproduction.

Thus, there has been described a novel system for providing stereophonic sound recording on narrow width moture equipment designed to accommodate both'Super 8 and conventional 8 mm. formats.

Although it has been suggested that thedifierence signal be recorded on the balance stripe" of Super 8 motion picture film, it is also contemplated that a stripe of simi- I lar width might be coated on other motion picture film in the corresponding,locatin,but'provided in such a manner as would augment therecording qualities thereof and also function to provide bal'ance.

While I have described and illustratedseveral specific embodiments of my invention, it will be clear that variation of the details of"con's'truction whichare specifically illustrated and described mayberesorted to without departing from thetrue spirit and scope of the invention as defined in the appended claims. a

I claim:

1. A compatible stereophonic sound system for motion pictures utilizing a photographic motion picture film having relatively wide and'narrow magneticstrips disposed along the length thereof, said filmiricluding sprocket holes adjacent one edge thereof, and wherein the relatively wide magnetic 'stripe "is disposed along the 'opposite edge of said film and wherein said relativelynarrow magnetic stripe is 20-65% as Wide assaid relatively wide magnetic stripe and is provided solely for mechanical balance of said film for'winding purposes and is of inadequate quality for normal sound recording and reproduction and is located'intermediate said sprocket holes and said one edge of said film, comprising: first means magnetically responsive to a first signal recorded on the wide stripe of said film, said first signal comprising the sum of a first and a second stereophonic'signal, second means magnetically responsive to a second signal recorded on the narrow stripe of said film, said second signal comprising the difference between said first and second stereophonic signals;

and means responsive'to said sum and dilference signals nals therefrom. i 1

2. The system of claim 1 wherein said first means comprises a first magnetic pickup head spaced so as to define one lateral side of a film transport path, and said second for conversion to said first and second stereophonic sigmeans comprising a second magnetic pickup head spaced so as to define the opposite lateral side of said film transport path.

3. The system of claim 2 wherein said first and second magnetic pickup heads are directly oppositely disposed along the lateral direction of said film transport path.

4. The system according to claim ;1 wherein said means responsive to said sum and difference signals comprises a matrix having two outputs, each'output corresponding to one of "said two stereophonic signals, and means responsive to each of said stereophonic signals comprising an electroacoustic translator.

5. The system according to claim 1 wherein said means responsive to said sum and difference signals comprises amplifier'meansj said amplifier means comprising transformer means having a centertapped secondary winding for providing said sum signal with one and opposite polarity; two'loudspeaker means serially connected in circuit relation with'said winding and having a connection therebetween; means applying said difference signal between the connection of the two-series connected loudspeaker means and said centertap whereby said difference signal is combined with said sum signal of one and opposite polarity to produce an input of said first stereophonic signal to'one loudspeaker means and saidsecond stereophonic signal to the other loudspeaker means.

6, A compatible stereophonic sound system for motion pictures utilizing a motion picture filmhaving relatively Wide and narrow magnetic stripes disposed along the length thereof, said narrow stripe being of insuflicient width to provide high fidelity sound reproduction, said film including sprocket holes adjacent one edge thereof, and wherein the relatively wide magnetic stripe is disposed along the opposite edge of said film and'wherein said relatively narrow magnetic stripe 'is 20-65% as wide as said relatively wide magnetic stripe and is provided solely for mechanical balance of said film for winding pur- 'said film, said difference signal comprising the difference between said first and second stereophonic signals, means responsive to the amplitude of said sum signal for diminishing the amplitude of said difference signal whenever the amplitude of said sum signal is lower than a predetermined value; and means responsive to said sum and difference signals for decomposition into said first and second stereophonic signals.

References Cited UNITED STATES PATENTS 2,673,248 3/1954 Hamberg 179l00.2 4 2,786,894 3/1957 Gunby 179-1001 3,017,466 1/196-2 Kerr 352-37 2/1963 Owen et al 179---100.4

' OTHER REFERENCES Electronics World (January 1960), 179/ 100.4, pp. 50, 156, 157.

BERNARD KONICK, Primary Examiner.

JEROME P. MULLINS, Assistant Examiner.

US. Cl. X.R. 

